This invention relates to a gear set and more particularly to a parallel axis gear set in which shocks and noise due to the backlash between gears is reduced. It also relates to an elevator hoist employing such a parallel axis gear set.
A conventional elevator hoist apparatus has a speed reduction gear connected between an electric motor and a hoist drum. The speed reduction gear generally is a parallel axis speed reduction gear having a first spur gear and a second spur gear in engagement with the first gear. The first gear has a first shaft connected to the motor, and the second gear has a second shaft parallel to the first shaft and connected to the hoist drum.
The hoist drum has a plurality of elevator main ropes wound therearound. An elevator car is connected to one end of the main ropes and a counterweight is connected to the other end of the main ropes. When the elevator car is to be selectively moved upward or downward or stopped or started within the hoistway, the speed and the direction of rotation of the drum is changed. Since the elevator car and the counterweight are connected to the opposite ends of the main ropes, they move in opposite directions relative to each other.
When the elevator car is started and accelerated from a complete stop to a predetermined constant speed or decelerated to serve at a floor, or when the direction of movement of the car is changed at the ends of the hoistway, the rotational speed or direction of the input shaft and therefore the speed of the driving gear of the speed reduction gear must be changed. Upon such a change in the rotation of the speed of the driving gear, the gear teeth of the driving gear hit the gear teeth of the driven gear due to backlash between the driving teeth and the driven teeth. This also takes place when the load on the elevator car and the counterweight balance each other and when the load on the car changes.
Such hitting between the driving and driven gear teeth due to backlash is disadvantageous in that the shocks and noise are generated in the speed reduction gear, and the precise positioning of the elevator car at the landing cannot be realized. Particularly, when shocks are generated between the driving and driven gears due to backlash the shocks are transmitted through the main ropes to the elevator car significantly degrading the comfort of the passengers in the elevator car.